Lumps in breasts. I'm scared.

This is my first post ever. I'm 36 with an amazing 5 year old son and husband. I had my annual mammogram on December 10th (I have very dense and fibrous breast tissue, so my gyno had me start getting mammograms at 35) 6 days later I felt a lump in my right breast. I went in for a breast exam today just to be sure everything was okay. My gyno found a smaller lump in my left breast. He's sending me to have an ultrasound of both breasts on January 7th. I'm terrified. I recently found out from my mom that her maternal grandmother had breast cancer. A fact I had previously been unaware of. What has yourexperience been with finding a lump(s) in your breast(s)?